Apparatus for transmitting motion to mold sections in injection molding machines

ABSTRACT

Clamping apparatus for an injection molding machine wherein a movable platen is reciprocable between a fixed platen and a support for a stationary mold section has at least one pair of toggle links whose outer ends are pivoted to the two platens and whose inner ends are pivoted to each other, at least one pair of levers the outer ends of which are pivoted to the platens and the inner ends of which are pivoted to each other, and a hydraulic motor having a cylinder which is pivotally connected to at least one of the levers and a piston rod pivotally connected to the pin coupling the inner ends of the toggle links. When the movable platen is remote from the support, the toggle links make with each other an angle of less than 90* and the piston rod of the hydraulic motor makes with the tie rods for the movable platen an acute angle which is preferably less than 45*. This insures the generation of a substantial closing force as soon as the movable platen begins to advance toward the support and prevents excessive acceleration or deceleration of the movable platen during movement away from or toward the fixed platen.

3,736,092 May 29, 1973 APPARATUS FOR TRANSMITTING MOTION TO MOLDSECTIONS IN INJECTION MOLDING MACHINES Inventors: Karl Kiinig, Munich;Ernst Wiirl, Weiboldshausen; Richard Herbst, Munich, all of GermanyAssignee: Krauss-Matfei Aktiengesellschaft,

Munich, Germany Filed: Apr. 8, 1971 Appl. No.: 132,466

Foreign Application Priority Data Apr. 11, 1970 Germany ..P 20 17 476.9

11.8. C1 ..425/450 Int. Cl. ..B29f l/00 Field of Search ..425/450, 242,247, 425/406, 408

References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS863,974 3/1961 Great Britain ..425/242 Primary Examiner-J. SpencerOverholser Assistant Examiner-David S. Safran AttorneyMichael S. Striker[57] ABSTRACT Clamping apparatus for an injection molding machinewherein a movable platen is reciprocable between a fixed platen and asupport for a stationary mold section has at least one pair of togglelinks whose outer ends are pivoted to the two platens and whose innerends are pivoted to each other, at least one pair of levers the outerends of which are pivoted to the platens and the inner ends of which arepivoted to each other, and a hydraulic motor having a cylinder which ispivotally connected to at least one of the levers and a piston rodpivotally connected to the pin coupling the inner ends of the togglelinks. When the movable platen is remote from the support, the togglelinks make with each other an angle ofless than 90 and the piston rod ofthe hydraulic motor makes with the tie rods for the movable platen anacute angle which is preferably less than 45. This insures thegeneration of a substantial closing force as soon as the movable platenbegins to advance toward the support and prevents excessive accelerationor deceleration of the movable platen during movement away from ortoward the fixed platen.

17 Claims, 12 Drawing Figures PATENTED 3. 7 36,092

SHEET 1 OF 4 Fig .1

INV ENTORS la komc BY Elm? vi) PATENTLDM 3,736,092

SHEET 2 OF 4 IN V EN TORS mm L k 61 BACKGROUND OF THE INVENTION Thepresent invention relates to improvements in clamping or motiontransmitting apparatus which can be utilized in machines for theproduction of injection molded articles to maintain a movable moldsection in a requisite clamping and sealing engagement with a secondmold section. More particularly, the invention relates to improvementsin clamping apparatus which can be used with particular advantage ininjection molding machines for the production of articles consisting ofsynthetic plastic material and wherein a movable platen is reciprocablealong tie rods extending between a stationary platen and a stationarysupport for a first mold section. The movable platen carries a secondmold section which must be held in clamping and sealing engagement withthe first mold section during injection and setting of plastic materialin the mold cavity. v,

German Pat. No. 1,116,386discloses a clamping apparatus which employs apair of toggle links, two levers and a hydraulic cylinder and pistonunit. The toggle links are pivoted to each other and to the two platens.The levers are pivoted to the two platens and to separate pins providedon the cylinder of the hydraulic unit. The axis of the cylinder isnormal to the direction of reciprocatory movement of the movable platenand the piston rod of the hydraulic unit is coupled to a pivot pin whichconnects the two toggle links to each other.

A drawback of such clamping apparatus is that the movable platen issubjected to excessive accelerating and decelerating forces duringmovement toward and away from the first mold section. Furthermore, thevariations in the magnitude of closing force which is furnished by thehydraulic unit and acts in a direction to urge the second mold sectiontoward the first mold section are unsatisfactory, especially when themovable platen starts its movement from the fully retracted position inwhich the mold is open. Moreover, the ratio of movement of the pistonrod to movement of the movpiston rod is very unsatisfactory because aminute axial displacement of the piston rod must bring about a verysubstantial displacement of the movable platen. This contributes to theaforementioned unsatisfactory values of closing force during the initialand closing stages of operation of the patented clamping apparatus. Afurther drawback of the patented clamping apparatus is that the forcewith which the movable platen is drawn to its retracted position duringthe last stage of the return stroke of the movable platen in very small;this is undesirable because the ejection of shaped articles from themold section on the movable platen normally takes place when the movableplaten approaches its fully retracted position.

SUMMARY OF THE INVENTION An object of the invention is to provide anovel and improved motion transmitting apparatus, particularly aclamping apparatus for the movable platen of an injecmolding machinesand is capable of furnishing more satisfactory closing, locking andopening forces than presently known clamping apparatus.

Another object of the invention is to provide a clamping apparatus whichis constructed and assembled in such a way that it prevents undesirableacceleration and/or deceleration of the part or parts which receivemotion therefrom, and which occupies less room and is more reliable,stronger and sturdier than presently known clamping apparatus having thesame dimensions.

A further object of the invention is to provide a clamping apparatuswhich can furnish a satisfactory closing force as soon as the movableplaten of an injection molding machine starts to leave its retractedposition in which the mold is open.

An additional object of the invention is to provide a clamping apparatuswhich is capable of moving the movable platen with a substantial forceduring the last stage of return movement of such platen to the retractedposition to thus insure that the movable platen cannot be decelerated orarrested during ejection of shaped articles from the cavity of themovable mold section by means of knockout pins or the like.

Another object of the invention is to provide a clamping apparatus whichcan insure uniform distribution of stresses on the platens and on theguide means for the movable platen.

A further object of the invention is to provide a clamping apparatuswherein the parts are interchangeable and wherein the number ofdifferent parts is relatively small to thus contribute to lower initialand maintenance cost.

j An ancillary object of the invention is to provide a clampingapparatus wherein the parts are readily accesible to thus insure that.the inspection, replacement and/or repair of parts can be completed withlittle loss in time.

The invention is embodied in a motion transmitting or clamping apparatuswhich is preferably used in an injection molding machine of the typehaving a first platen, elongated guide means preferably includingseveral parallel tie rods which are connected to and extend from thefirst platen, and a second platen which carries a movable mold sectionand is movable along the guide means between a first position nearer toand a second position remote from the first platen. The mold is open inthe first position and is closed in the second position of the secondplaten.

The clamping apparatus comprises first and second toggle links makingwith each other an angle of less than in the first position of thesecond platen and having first or outer ends pivoted to the first andsecond platens and second or inner ends pivoted to each other to form ajunction, a pair of levers having outer ends pivoted to the first andsecond platens and inner ends pivoted to each other, and a prime moverpreferably including a hydraulic or pneumatic motor having a cylinderpivoted to at least one of the levers (preferably to that lever which ispivoted to the first platen) and a piston rod which is pivoted to thelinks at the aforementioned junction. The angle between the path ofmovement of the piston rod in the first position of the second platenand the path for movement of the second platen from the first to thesecond position is less than 90,

preferably less than 71 and most preferably less than 45.

The second platen is caused to move to its second position in responseto movement of the outer end of the piston rod (junction between thetoggle links) away from the cylinder of the prime mover.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims.

The improved clamping apparatus itself, however, both as to itsconstruction and its mode of operation, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary longitudinalvertical sectional view of an injection molding machine and a sideelevational view of a motion transmitting or clamping apparatus which isused to reciprocate a movable platen of the injection molding machineand is constructed and assembled in accordance with a first embodimentof the invention, the section of FIG. 1 being taken in the direction ofarrows as seen from the line I-I of FIG. 3. 3;

FIG. 2 illustrates the structure of FIG. 1 but with the movable platenin a different positon in which the sections of the mold are clampedagainst each other;

FIG. 3 is a plan view of the structure shown in FIG.

FIG. 4 is a diagram with curves representing the speed of movement ofthe movable platen and certain other characteristics of injectionmolding machines which employ conventional clamping apparatus and theapparatus of FIGS. 1-3;

FIG. 4a is a diagrammatic fragmentary vertical sectional view of aninjection molding machine which is provided with a conventional clampingapparatus;

FIG. 5 is a fragmentary longitudinal vertical sectional view of aninjection molding machine and a side elevational view of a clampingapparatus which is constructed and assembled in accordance with a secondembodiment of the invention, the movable platen of the machine beingshown in a first position by solid lines and in a second position bybroken lines;

FIG. 6 is a fragmentary schematic side elevational view of an injectionmolding machine with the movable platen in a first position, and a sideelevational view of a third clamping apparatus;

FIG. 6a illustrates the structure of FIG. 6 but with the movable platenin a second position;

FIG. 7 is a fragmentary schematic side elevational view of an injectionmolding machine with the movable platen in a first position, and a sideelevational view of a fourth clamping apparatus;

FIG. 7a shows the structure of FIG. 7 but with the movable platen in asecond position;

FIG. 8 is a fragmentary schematic side elevational view of an injectionmolding machine with the movable platen in a first position, and a sideelevational view of a fifth clamping apparatus; and

FIG. 8a illustrates the structure of FIG. 8 but with the movable platenin a second position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 and2, there is shown a portion of an injection molding machine including astationary first platen l, a stationary support 3 which is spaced fromthe platen 1, elongated guide means including four parallel horizontaltie rods 12 which are connected to and extend from the first platen 1toward and through the support 3, and a movable second platen 2 which ismounted on the tie rods 12 and is reciprocable between a first position(shown in FIG. 1) nearer to and a second position (FIG. 2) remote fromthe first platen l. The support 3 is fixedly connected with a moldsection 5 which faces the second platen 2, and the 'second platen isfixedly connected with a complementary mold section 4 which faces themold section 5. The mold section 4 is forced into sealing engagementwith the mold section 5 when the platen 2 assumes the second position ofFIG. 2.

The injection molding machine the parts of which are shown in FIGS. 1and 2 is especially suited for use in the manufactureof shaped'articlesconsisting of synthetic plastic material which is introduced inplasticized state through a mouth 6 provided in the right-hand side ofthe support 2 to flow through one or more channels 7 provided in thesupport 3 and mold section 5, and to fill one or more mold cavitieswhich are defined by the mold sections 4, 5 in the second position ofthe movable platen 2..The thus injected plasticized material is thenallowed or causedto set and the resulting shaped article or articles areexpelled from the cavity by suitable knockout devices (not shown) notlater than when the movable piston 2 is returned to the first positionshown in FIG. 1 in which the mold is open. The mechanism for theplasticizing and for the injection of synthetic plastic material by wayof the mouth 6 and channel or channels 7 is of known design and itsconstruction and mode of operation form no part of this invention.

' The invention resides in the provision of a novel motion transmittingor clamping apparatus which is utilized to move the platen 2 between thepositions of FIGS. 1 and 2 and to hold the mold section 4 in theposition of FIG. 2 during injection of plasticized material and duringsetting of such material in the mold cavity or cavities. The improvedclamping apparatus comprises two toggle links 8, 9 of identical lengthwhich have first or outer ends respectively pivoted to the brackets 21,22 of the platens 1, 2 by horizontal pivot pins 23, 24 and second orinner ends which are pivoted to each other to form a junction by meansofa third horizontal pivot pin 25. It will be seen that, when themovable platen 2 dwells in the first position of FIG. 1, the anglebetween the toggle links 8 and 9 is less than 90, for example, about Themotion transmitting or clamping apparatus further comprises a primemover 28 and two additional links 10, 11 which will be called levers inorder to avoid confusion with the toggle links 8 and 9. The lever 10 isa straight lever and one of its ends is articulately connected to thebracket 22 of the movable platen 2 for pivotal movement about the pin24, i.e., about the pivot axis of the outer end of the toggle link 9.The other lever l 1 is a bell crank having two substantially straightarms 11a, 1112 which preferably make an angle of at least close to andwhose outer ends respectively constitute the first and second ends ofthe lever 11. The free end of the arm 11a is coupled to the bracket 21to pivot about the axis of the pin 23, and the free end of the arm 11bis articulately connected to the inner end of the lever 10 by a pivotpin 26 which is parallel to the pivot pins 23, 24 and 25. Those edgefaces 11c, 11d of the arms 11a, 11b which are remote from the pivot pins23, 26 are of arcuate shape so that the lever 11 resembles a boomerangwith the arm 11a slightly longer than the arm 11b.

The prime mover 28 is a hydraulically or pneumatically operated motorhaving a first portion or cylinder 29 which is articulately connectedwith an intermediate portion of the bell crank lever 11 by a horizontalpivot pin 27 parallel to the pins 23-26 and located in the region of theapex of the lever 11. The second portion of the prime mover 28 includesan elongated piston rod 33 and a piston 30 which is rigid with the innerend of the piston rod 33 and is reciprocable in the cylinder 29 betweentwo fluid-conveying ports 31, 32. The cylinder 29 is of thedouble-acting type, i.e., the piston rod 33 is expelled to move theplaten 2 to the second position of FIG. 2 in response to admission of apressurized fluid by way of the port 31, and the piston rod 33 isretracted to return the platen 2 to the first position of FIG. 1 inresponse to admission of pressurized fluid by way of the port 32.

In accordance with a further feature of the invention, the direction ofmovement of the piston rod 33 (i.e., the path of movement of the pivotpin 25 at the junction between the toggle links 8, 9) and the directionof movement of the movable platen 2 from the first position shown inFIG. 1 (i.e., the straight line path defined for the platen 2 by the tierods 12) make an acute angle which is preferably less than 71 and mostpreferably less than 45. In the embodiment of FIGS. 1 and 2, the anglebetween the straight line path for the platen 2 (for movement from theposition of FIG. 1 toward the position of FIG. 2) and the path for thepiston rod 33 is about 37.5.

FIG. 1 further shows that the movable platen 2 is provided with bearingsleeves 13 which surround the tie rods 12 and that the end portions ofthe tie rods 12 are provided with external threads. Furthermore, the tierods 12 have flanges 14 which abut against the lefthand face of thesupport 3 and the tie rods mesh with nuts 15 which abut against theright-hand face of the support 3. The externally threaded left-hand endportions 16 of the tie rods 12 mesh with nuts 17 which are rotatablymounted in the stationary platen 1, and such rotary nuts are connectedwith gears 20 meshing with a gear 19 on a horizontal adjusting shaft 18.The latter can be rotated by a handwheel or by a servomotor (not shown)to move the platen 1 nearer to or further away from the support 3. Suchadjustment might become necessary when the mold sections 4, 5 arereplaced with larger or smaller mold sections and/or when it isnecessary to move the platen 2 to the left beyond the first positionshown in FIG. 1.

The bearing brackets 21, 22 are disposed substantially midway betweenthe upper and lower tie rods 12, i.e., in the region of the resultant offorces which tend to move the platen 2 away from the second positionshown in FIG. 2 during injection and setting of plastic material in thecavity of the mold. When the movable platen 2 assumes the position ofFIG. 2, the toggle links 8, 9 are aligned or substantially aligned asshown in FIG. 2 by solid lines. Thus, the axis of the pivot pin 25 isthen located in or close to the common plane of the axes of pivot pins23, 24. If desired, the piston rod 33 can be movedoutwardly beyond thesolid-line position of FIG. 2 to maintain the toggle links 8, 9 inpositions 34 which are indicated in FIG. 2 by broken lines. This insuresthat the prime mover 28 cannot be subjected to any appreciable stressesduring injection of plasticized synthetic material into the mold cavity.The platen l is stationary while the platen 2 is moved by the links 8, 9and levers 10, 11 so that it acts as a component against which the parts8, 11 react during application of the closing and sealing forces.

The distance between the pivot pins 23, 26 (effective length of the bellcrank lever 11) exceeds the distance between the pivot pins 24, 26(effective length of the lever 10).

FIG. 3 illustrates the structure of FIG. 2 in a plan view, i.e., withthe movable platen 2 in the second position. It will be noted that themotion transmitting or clamping apparatus may comprise as many as fourtoggle links 8, two toggle links 9, two bell crank levers 11 and twostright levers 10. This insures more uniform distribution of stressesand enables the apparatus to transmit substantial closing and sealingforces without excessive stressing of the pivot pins and/or tie rods. Asshown, each of the bearing brackets 21, 22 may consist of severalaligned portions which support the ends and median portions of therespective pivot pins 23, 24. The structure of FIG. 3 employs twodiscrete coaxial pivot pins 26, a single elongated pivot pin 25, and twocoaxial pivot pins 27, one for each of the two bell crank levers 11. Theprime mover 28 is supported exclusively by the toggle links and levers,i.e., by the pivot pin 25 and by the pivot pins 27.

Prior to discussing the diagram of FIG. 4, reference will be had to FIG.4a which illustrates a conventional apparatus for reciprocating amovable platen 57 relative to a fixed platen 57a in directions indicatedby a double-headed arrow 46. The toggle links are shown at 40 and 41,the levers at 42, 43, the pivots where the levers 42, 43 arerespectively connected to the cylinder 45 of a hydraulic motor at 47, 48and the piston rod at 44. .The axis of the piston rod 44 is normal tothe direction indicated by the arrow 46 in all positions of the movableplaten 57. It will be noted that the levers 42, 43 of the conventionalapparatus are not directly coupled to each other but are connected totwo discrete parallel (not coaxial) pivot pins 47, 48 on the cylinder45.

FIG. 4a shows by solid lines changes in the speed of movement of themovable platen 2 while the piston rod 33 moves with reference to thecylinder 29, the changes in closing force which is furnished by theprime mover 28 during movement of the platen 2 toward the secondposition of FIG. 2, and the ratio of the extent of movement of thepiston rod 33 to the extent of movement of the platen 2. The broken-linecurves of FIG. 4a indicate the corresponding values for the conventionalclamping apparatus of FIG. 4a.

The changes in speed of the movable platen 57 of the conventionalapparatus of FIG. 4a are indicated by the curves 49b and 49. It will beseen that the speed of the platen 57 rises abruptly from zero speed tomaximum speed during the initial stage of movement of the piston rod 44in an upward direction, as viewed in FIG. 4a. The peak value 50 of thespeed of the platen 57 is reached almost immediately after the pistonrod 44 leaves the starting position of FIG. 4a. By using concretevalues, the peak value 50 can reach centimeters per second before themovable platen 57 completes one percent of its stroke toward theposition corresponding to that of the movable platen 2 shown in FIG. 2.From there on, the speed of movement of the platen 57 in theconventional machine decreases very rapidly as indicated by the portion49 of the speed curve. Such rapid rise and rapid decrease in the speedof the movable platen 57 are attributable to the relatively small ratiobetween the stroke of the piston rod 44 and the stroke of the platen 57;this ratio is indicated by the broken-line curve 51 of FIG. 4. The curve51 indicates that the acceleration of movable platen 57 necessitates theapplication of a considerable force. The changes in the magnitude ofsuch force for the conventional apparatus of FIG. 4a are represented bythe broken-line curve 52 of FIG. 4. The curve 52 shows that the forcerises very gradually from a relatively small initial value.

The speed of the movable platen 2, the ratio of the strokes of pistonrod 33 and platen 2, and the changes in the magnitude of closing andsealing force are more satisfactory in the machine which employs theclamping apparatus of FIGS. 1 and 2. As indicated by the curve 53b, 53of FIG. 4, the accelerating f the platen 2 as a function of the extentof movement from the first position of FIG. 1 is more gradual (comparewith the curve 49b, 49) and the peak value 54 of such speed is less thanhalf the peak value (50) of the speed of platen 57 in the conventionalclamping apparatus. Referring to the aforementioned example, the maximumspeed (54) of the platen 2 will be about 50 centimeters per second.Furthermore, the speed of the platen 2 rises to and decreases from suchmaximum value at a substantially constant rate and gradually to thusavoid undesirable peaks of acceleration or deceleration. This bringsabout savings in time and prevents excessive stressing of the links,levers, prime mover, tie rods and movable platen. The platen 2 reachesthe maximum speed (54) when it completes about 45 percent of its stroketoward the position of FIG. 2, i.e., substantially midway between thepositions of FIGS. 1 and 2. Such advantageous changes in the speed ofthe platen 2 influence the other values which were discussed inconnection with the apparatus of FIG. 4a. Thus, the ratio of the strokeof the piston rod 33 to the stroke of the platen 2 (curve 55 of FIG. 4)is relatively high all the way to the point when the toggle links 8, 9approach the positions of FIG. 2. The'changes in closing force arerepresented by the curve 56 of FIG. 4; it will be seen that the closingforce is greater at the start of movement of the platen 2 from theposition of FIG. 1 and is thereupon constant during a substantial partof a working stroke of the platen 2 to rise rapidly when the platenapproaches the position of FIG. 2. It is desirable to furnish arelatively large closing force at the very start of movement of theplaten 2 toward the position of FIG. 2 and at the very end of movementtoward the position of FIG. 1 (compare the left-hand portions of thecurves 52 and 56 in FIG. 4). v

The curves 49a, 53a which are shown by thin broken and solid linesrespectively indicate theoretical acceleration of the platens 57 and 2from their first positions, I

i.e., by disregarding the inertia of the masses of moving parts andfriction.

The generation of a substantial closing force (curve 56 of FIG. 4)immediately after the platen 2 starts its movement toward the positionof FIG. 2 is due to the novel mounting of the prime mover 28, i.e., tothe fact that the axes of the tie rods 12 (straight line path for theplaten 2) and the axis of the piston rod 33 make an acute angle which ispreferably less than 71 and most preferably less than 45. Thus the forcefurnished by the prime mover 28 in response to admission of pressurizedfluid via port 31 has a substantial component which acts on the platen 2in a direction to move this platen toward the support 3. This is indirect contrast to the teaching of prior art, as evidenced by theconstruction of the conventional clamping apparatus shown in FIG. 4a,wherein the direction of movement of the piston rod (44 in FIG. 4a) isalways normal to the direction of movement of the movable platen (57).Combined with the feature that the angle between the toggle links 8, 9in the first position of the platen 2 is less than 90, the arrangementof FIGS. 1 and 2 insures that the force acting on the pivot pin25 duringthe initial stage of movement of the platen 2 from the position of FIG.1 has a component which acts in the longitudinal direction of the tierods 12 and is greater than the component which is normal to the tierods. The component which in the longitudinal direction of tie rods 12would be smaller than the other component if the angle between thetoggle lines 8, 9 in the first position of the platen 2 would exceed 90.Another advantage of toggle links which make an acute angle when thesecond platen dwells in the first position is that the stroke of thesecond platen is longer. This will be readily understood with referenceto FIGS. 1 and 2; were the angle between the links 8, 9 shown in FIG. 1an obtuse angle, the platen 2 would cover a shorter distance in responseto movement of the links 8, 9 to the solid-line positions of FIG. 2.

The clamping apparatus of FIGS. 1 and 2 can operate properly andconstitutes an improvement over the conventional apparatus of FIG. 4aeven if the angle between the axis of the piston rod 33 and the axis ofa tie rod 12 is only slightly less than 90. However, in actual practice,and by taking into consideration such factors as friction and theinertia of moving parts, the effect is much more satisfactory if theangle between the axis of the piston rod 33 and the axis of a tie rod 12(in the first position of the movable platen 2) is substantially lessthan 90, preferably less than 71 and most preferably less than 45. Theefficiency of the improved apparatus increases with increasing value ofthe sine of the angle 90 minus alpha wherein alpha is the angle betweenthe axis of the piston rod 33 a plane which is normal to the tie rods12. When the angle alpha increases to 20, i.e., when the angle betweenthe axis of the piston rod 33 and a tie rod 12 is 70 or less, theclosing force (curve 56 in FIG. 4) becomes highly satisfactory duringmovement of the platen2 toward its second position to close the mold ofthe injection molding machine. The closing force is particularlysatisfactory when the axis of the a piston rod 33 is substantiallynormal to the line connecting the pivot pins 23, 26 at the ends of thebell crank lever 11, i.e., of that lever which is not directly connectedto the movable platen 2. p

An important advantage of the feature that the first portion or cylinder29 of the primer mover 28 is con-' nected with the lever 11 by a singlepivot 27 or by two coaxial pivots (see FIG. 3) is that the prime moveris not subjected to any appreciable shearing or like forces while theplaten 2 moves from the position of FIG. 1 to the position of FIG. 2 orvice versa. Such transverse forces are an important factor in the designof the prime mover for conventional clamping apparatus of the type shownin FIG. 40 (see the parallel pivot pins 47 and 48). In the clampingapparatus of the present invention, the cylinder 29 is pivotable withreference to the lever 11 about a single axis (pivot pin 27) and,therefore, this cylinder cannot be subjected to any appreciable shearingor other deforming stresses. Of course, if the apparatus of the presentinvention employs an exceptionally rugged prime mover which is capableof withstanding substantial shearing or like deforming stresses, theprovision ofa single pivot (pin 27) between the lever of levers of theclosing apparatus and the cylinder of the prime mover is of lesserimportance. However, when the prime mover employs a hydraulic orpneumatic cylinder and piston unit, the shearing and like stresses aresufficiently important to warrant the mounting of the cylinder in amanner as shown in FIGS. 1 to 3, i.e., in such a way that the lever 11can pivot with reference to the cylinder 29 about a single pivot axis orvice versa.

The positions of the cylinder 29 and piston rod 33 can be reversed,i.e., the cylinder can be pivotally connected with the pin 25.

An advantage of the provision of a boomerangshaped bell crank lever (11)with substantially straight arms (11a, 11b) which make an angle of 90 orclose to 90 is that the levers 10, 11 need not overlap the toggle links8, 9. This is often desirable to insure satisfactory utilization ofspace, especially if the clamping apparatus comprises several pairs oflevers and/or toggle links (see FIG. 3)

FIG. 5 illustrates a portion of an injection molding machine (with firstand second platens 64, 65 and guide means including tie rods 78, 79)which embodies a modified clamping apparatus having toggle links 60, 61and levers 74, 73 which respectively correspond to the parts 8, 9 and10, 11 of FIGS. 1 and 2. The cylinder 76 of the prime mover is pivotedto an intermediate portion of the bell crank lever 73 by a pin 75, andthe outer end of the piston rod 77 of the prime mover is pivoted to thepin 70 at the junction of the toggle links 60 and 61. The pivot pins 66,68 for the outer ends of the links 60, 61 are mounted in first or lowerbrackets 64a, 65a of the platens 64, 65. These platens further compriseupper bearing brackets 64b, 65b for horizontal pivot pins 67, 69 servingto pivotally support the outer ends of two additional toggle links 62,63 which are respectively parallel to the links 60, 61 and are connectedto each other at their inner ends to form a second junction (see the pin71). The pivot pins 70 and 71 are coupled to each other by a connectorlink 72. The length of all four toggle links 60-63 is the same. As shownin FIG. 5, the angle between the toggle links 60, 61 or 62, 63 in thefirst (solid-line) position of the movable platen 65 is substantiallyless than 90 and the angle between the axis of the piston rod 77 of theprime mover (preferably a hydraulically operated cylinder and pistonunit) and the axes of the tie rods 78,79 is also substantially less than90. The outer ends of the levers 73, 74 are pivotally connected to thelower brackets 64a, 65a, i.e., to those brackets which are nearer to theprime mover.

The structure of FIG. 5 is desirable when the clamping apparatus mustfurnish a substantial closing force and when the stresses upon theplanes 64, 65 and tie rods 78, 79 must be distributed more uniformly.For example, the clamping apparatus of FIG. 5 can be used when thecavity defined by the mold sections respectively carried by the support3 and platen 65 is of such configuration that different portions of theplaten 65 are subjected to stresses of different magnitude while theclamping apparatus furnishes the closing and sealing forces. The featurethat the bearing brackets 64a, 64b and 65a, 65b are located at aconsiderable distance from each other and that the apparatus comprisestwo pairs of toggle links 60, 61 and 62, 63 which are respectivelypivoted to the uper and lower bearing brackets reduces the likelihood ofexcessive bending stresses upon the tie rods 78, 79 and prevents atilting of the movable platen 65. Furthermore, since the levers 73, 74are pivoted to the lower bearing brackets 64a, 65a, the prime mover isreadily accessible below the path for the movable platen 65.

FIGS. 6 and 6a illustrate portions of an injection molding machine withstationary and movable platens 91, 92 and a third clamping apparatuswhich employs two straight levers 85, 86. The positions of the movableplaten 92 in FIGS. 6 and 6a respectively correspond to the first andsecond positions of the platen 2 shown in FIGS. 1 and 2. The two pairsof toggle links -81 and 82-83 and the connector link 84 respectivelycorrespond to the parts 60-61, 62-63 and 72 of the apparatus shown inFIG. 5. The pivot pins for the outer ends of the toggle links 80-83 arerespectively shown at 89, 89a, 89b, 890, the pivot pin at the junctionof the links 80, 81 at 94, the pivot pin at the junction of links 82, 83at 94a, the pivot pin which connects the levers 85, 86 to each other at93, and the pivot pins which connect the outer ends of the levers 85, 86to the lower brackets of the platens 91, 92 at 90 and 90a.

It will be noted that the outer ends of the levers 85, 86 are pivotableabout axes (defined by the pivot pins 90, 90a) which do not coincidewith the pivot axes for the outer ends of the links 80, 81 or 82, 83.Furthermore, the cylinder 88 of the prime mover is pivoted to the leverby the aforementioned pin 93 which simultaneously connects the lever 85to to the lever 86. The cylinder 88 is preferably a double-actinghydraulic cylinder and the piston rod 87 is connected to the pin 94. Anadvantage of the apparatus of FIGS. 6 and 6a is that it does not have touse the pivot pin 75 of FIG. 5. The provision of discrete pivot pins 90,a for the outer end of the levers 85, 86 contributes to more uniformdistribution of stresses. 9

A feature of the clamping apparatus which is shown in FIGS. 7 and 7a isthat the length of the lever 98 equals the length of the lever 97.Otherwise, the clamping apparatus of FIGS. 7 and 7a is identical withthe apparatus of FIGS. 1 and 2. The toggle links are shown at 95, 96,the cylinder of the prime mover at 99, and the pivot pin between thecylinder 99 and an intermediate portion of the lever 97 at 100. The costof the apparatus of FIGS. 7 and 7a is rather low because the levers 97and 98 are not identical size and shape. The character 98a denotes ahole or bore which is provided in the lever 98 to receive the pivot pin100 if the lever 98 is to be used in place of the lever 97.

The length of the toggle link 95 equals that of the toggle links 96.

FIGS. 8 and 8a illustrate the platens 109, 110 of an injection moldingmachine which employs a further clamping apparatus for the movableplaten 110. This apparatus is more compact than the previously describedapparatus because the cylinder of the prime mover is connected to theintermediate portion of the bell crank lever 106 by a pivot pin 108located at a point which is remotest from the junction between thetoggle links 101, 102, i.e., which is remotest from the outer end of thepiston rod 105a. The characters 103, 104 respectively denote the togglelinks of the second pair, the straight lever is shown at 107, and thepivot pin which connects the inner ends of the levers 106, 107 to eachother is shown at 111. It will be noted that the clamping apparatus ofFIGS. 8 and 8a is similar to the apparatus of FIG. excepting that theouter ends of the levers 106, 107 are pivotable on separate pins 112,113 and that the cylinder 105 does not extend beyond the apex of thebell crank lever 106. When the platen 110 assumes the first positionshown in FIG. 8, the pivot pin 108 is located substantially midwaybetween the platens 109, 110. The bell crank lever 106 does not have toextend well below the lower tie rods (not shown in FIGS. 8 and 8a), evenwhen the platen 110 dwells in the first position of FIG. 8, because theouter ends of the levers 106, 107 are coupled to the platens 109, 110substantially midway between the pivots for the outer ends of the upperlinks 101, 102 and lower links 103, 104.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art and, therefore, suchadaptions should and are intended to be comprehended within the meaningand range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is:I

1. In an injection molding machine, the combination of a first platen;elongated guide means extending from said first platen; a second platenmovable with reference to said guide means along a first straight linepath between a first position nearer to and a second position remotefrom said first platen; and apparatus for moving said second platen,comprising first and second toggle links making with each other an acuteangle in the first position of said second platen and having first endsrespectively pivoted to said first and second platens and second endspivoted to each other to form a first junction, first and second levershaving first ends respectively pivoted to said first and second platensand second ends pivoted to each other to form a second junction, saidfirst lever being a bell crank having a concave side facing said secondplaten and the distance between said first and second ends of said firstlever being greater than the distance between said first and second endsof said second lever, and a prime mover including a first portionpivotally connected with said first lever intermediate said first andsecond ends thereof and with said second junction, said prime moverfurther including a second portion pivotally connected to said firstjunction and movable relative to said first portion along a secondstraight line path which makes an angle of less than 71 with said firstpath in the first position of said second platen to thereby move saidsecond platen toward said second position by displacing said firstjunction in a direction to enlarge the angle between said links.

2. The combination of claim 1, wherein the angle between said first andsecond paths in the first position of said second platen is less than 45degrees.

3. The combination of claim 1, wherein the second ends of said leversare pivotable about said axis.

4. The combination of claim 1, wherein said levers are of identicallength.

5. The combination of claim 4, further comprising pivot meansarticulately connecting said first portion of said prime mover to saidfirst lever intermediate said first and second ends of said first lever.

6. The combination of claim 5, wherein said links are of identicallength which is less than the length of said levers.

7. The combination of claim 1, wherein the distance between the saidfirst and second ends of said first lever is greater than the distancebetween said first and second ends of said second lever and wherein saidlinks are of identical length, and further comprising pivot meansarticulately connecting said first portion of said prime mover to saidfirst lever intermediate the first and second ends of said first lever.

8. In an injection molding machine, the combination of a first platen;elongated guide means extending from said first platen; a second platenmovable with reference to said guide means along a first straight linepath between a first position nearer to and a second position remotefrom said first platen; and apparatus for moving said second platen,comprising first and second toggle links making with each other an acuteangle in the first position of said second platen and having first endsrespectively pivoted to said first and second platens and second endspivoted to each other to form a first junction, first and second levershaving first ends respectively pivoted to said first and second platensand second ends pivoted to each other to form a second junction, thefirst ends of said first link and said first lever being pivotable withreference to said first platen about a first common pivot axis, and thefirst ends of said second link and said second lever being pivotablewith reference to said second platen about a second common pivot axiswhich is parallel to said first axis, and a prime mover including afirst portion pivotally connected with one of the two elements includingsaid first lever and said second junction and a second portion pivotallyconnected to said first junction and movable relative to said firstportion along a second straight line path which makes an angle of lessthan 71 with said first path in the first position of said second platento thereby move said second platen toward said second positon bydisplacing said first junction in a direction to enlarge the anglebetween said links.

9. The combination of claim 8, wherein said bell crank has two armsmaking an angle of about 10. The combination of claim 9, wherein saidarms of said bell crank have outer ends respectively constituting thefirst and second ends of said first lever and fur ther comprising pivotmeans articulately connecting said first lever with said first portionof said prime mover in the region of the apex of said bell crank, saidouter ends being of identical length.

l 1. The combination of claim 8 wherein said apparatus further comprisesthird and fourth links respectively parallel to said first and secondlinks and having first end respectively pivoted to said first and secondplatens and second ends pivoted to each other to form a third junction.

12. The combination of claim 11, further comprising a connector linkcoupling said first junction with said third junction.

13. The combination of claim 11, wherein said first ends of said firstlink and said first lever are pivotable with reference to said firstplaten about a first pivot axis and the first ends of said second linkand said second lever are pivotable with reference to said second platenabout a second pivot axis which is parallel to said first axis.

14. The combination of claim 13, wherein the first ends of said thirdand fourth links are respectively pivotable with reference to said firstand second platens about third and fourth pivot axes which are parallelto said first and second axes.

15. The combination of claim 8, wherein said first portion of said primemover is a double-acting cylinder and said second portion includes apiston rod having a piston which is reciprocable in said cylinder.

16. The combination of claim 8, wherein said guide means comprises aplurality of parallel tie rods and said first and second portions ofsaid prime mover are respectively pivotable relative to said firstjunction and said first lever, and further comprising a support remotefrom said first platen and connected with said tie rods, a first moldsection mounted on said support and facing said second platen, and asecond mold section mounted on said second platen and facing said firstmold section, said second mold section engaging said first mold sectionin the second position of said second platent.

17. The combination of claim 1, wherein the angle between said first andsecond paths in the first position of said second platen is less than45.

1. In an injection molding machine, the combination of a first platen;elongated guide means extending from said first platen; a second platenmovable with reference to said guide means along a first straight linepath between a first position nearer to and a second position remotefrom said first platen; and apparatus for moving said second platen,comprising first and second toggle links making with each other an acuteangle in the first position of said second platen and having first endsrespectively pivoted to said first and second platens and second endspivoted to each other to form a first junction, first and second levershaving first ends respectively pivoted to said first and second platensand second ends pivoted to each other to form a second junction, saidfirst lever being a bell crank having a concave side facing said secondplaten and the distance between said first and second ends of said firstlever being greater than the distance between said first and second endsof said second lever, and a prime mover including a first portionpivotally connected with said first lever intermediate said first andsecond ends thereof and with said second junction, said prime moverfurther includiNg a second portion pivotally connected to said firstjunction and movable relative to said first portion along a secondstraight line path which makes an angle of less than 71* with said firstpath in the first position of said second platen to thereby move saidsecond platen toward said second position by displacing said firstjunction in a direction to enlarge the angle between said links.
 2. Thecombination of claim 1, wherein the angle between said first and secondpaths in the first position of said second platen is less than 45degrees.
 3. The combination of claim 1, wherein the second ends of saidlevers are pivotable about said axis.
 4. The combination of claim 1,wherein said levers are of identical length.
 5. The combination of claim4, further comprising pivot means articulately connecting said firstportion of said prime mover to said first lever intermediate said firstand second ends of said first lever.
 6. The combination of claim 5,wherein said links are of identical length which is less than the lengthof said levers.
 7. The combination of claim 1, wherein the distancebetween the said first and second ends of said first lever is greaterthan the distance between said first and second ends of said secondlever and wherein said links are of identical length, and furthercomprising pivot means articulately connecting said first portion ofsaid prime mover to said first lever intermediate the first and secondends of said first lever.
 8. In an injection molding machine, thecombination of a first platen; elongated guide means extending from saidfirst platen; a second platen movable with reference to said guide meansalong a first straight line path between a first position nearer to anda second position remote from said first platen; and apparatus formoving said second platen, comprising first and second toggle linksmaking with each other an acute angle in the first position of saidsecond platen and having first ends respectively pivoted to said firstand second platens and second ends pivoted to each other to form a firstjunction, first and second levers having first ends respectively pivotedto said first and second platens and second ends pivoted to each otherto form a second junction, the first ends of said first link and saidfirst lever being pivotable with reference to said first platen about afirst common pivot axis, and the first ends of said second link and saidsecond lever being pivotable with reference to said second platen abouta second common pivot axis which is parallel to said first axis, and aprime mover including a first portion pivotally connected with one ofthe two elements including said first lever and said second junction anda second portion pivotally connected to said first junction and movablerelative to said first portion along a second straight line path whichmakes an angle of less than 71* with said first path in the firstposition of said second platen to thereby move said second platen towardsaid second positon by displacing said first junction in a direction toenlarge the angle between said links.
 9. The combination of claim 8,wherein said bell crank has two arms making an angle of about 90*. 10.The combination of claim 9, wherein said arms of said bell crank haveouter ends respectively constituting the first and second ends of saidfirst lever and further comprising pivot means articulately connectingsaid first lever with said first portion of said prime mover in theregion of the apex of said bell crank, said outer ends being ofidentical length.
 11. The combination of claim 8, wherein said apparatusfurther comprises third and fourth links respectively parallel to saidfirst and second links and having first ends respectively pivoted tosaid first and second platens and second ends pivoted to each other toform a third junction.
 12. The combination of claim 11, furthercomprising a connector link coupling said first junction with said thirdjunction.
 13. The combination of claim 11, wherein said first ends ofsaid first link and said first lever are pivotable with reference tosaid first platen about a first pivot axis and the first ends of saidsecond link and said second lever are pivotable with reference to saidsecond platen about a second pivot axis which is parallel to said firstaxis.
 14. The combination of claim 13, wherein the first ends of saidthird and fourth links are respectively pivotable with reference to saidfirst and second platens about third and fourth pivot axes which areparallel to said first and second axes.
 15. The combination of claim 8,wherein said first portion of said prime mover is a double-actingcylinder and said second portion includes a piston rod having a pistonwhich is reciprocable in said cylinder.
 16. The combination of claim 8,wherein said guide means comprises a plurality of parallel tie rods andsaid first and second portions of said prime mover are respectivelypivotable relative to said first junction and said first lever, andfurther comprising a support remote from said first platen and connectedwith said tie rods, a first mold section mounted on said support andfacing said second platen, and a second mold section mounted on saidsecond platen and facing said first mold section, said second moldsection engaging said first mold section in the second position of saidsecond platen.
 17. The combination of claim 1, wherein the angle betweensaid first and second paths in the first position of said second platenis less than 45*.